In the context of a katana, the term "hamon" refers to the distinct temper line that is visible on the blade. The hamon is a result of the differential hardening process used in traditional Japanese swordmaking, known as "yaki-ire." It is a visual pattern that separates the hardened cutting edge (yakiba) from the softer, more flexible spine (mune) of the blade.

The formation of the hamon involves carefully controlling the heating and cooling of the blade during the quenching process. The blade is heated and then rapidly cooled by immersing it in water or oil. The differential cooling rate results in varying hardness and resilience across the blade, giving rise to the hamon.

The hamon can exhibit various patterns, each with its own aesthetic appeal. Some common hamon patterns include:

1. Chōji: This pattern resembles the shape of cloves and often features large, rounded, and irregular patterns along the blade.
2. Gunome: This pattern consists of repeated semi-circular or irregular waves along the blade.
3. Suguha: This pattern is characterized by a straight and uninterrupted line.
4. Notare: This pattern features large, graceful waves that flow along the blade.

The hamon not only adds visual beauty to the katana but also serves as an indication of the skill and craftsmanship of the swordsmith. It is considered one of the distinguishing features of a well-made and traditionally crafted katana.